<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div id="app">
    <input id="msg" type="text" name="msg" onkeyup="show()">
    <div id="rst">

    </div>
</div>



<script type="text/javascript">
    document.getElementById("");
    show=()=>{
        document.getElementById("rst")
    }
</script>
</body>
</html>